The rapid growth of both the number of connected devices, and the data volume that is expected to be associated with IoT applications, has increased the popularity of Machine-to-Machine (M2M) type communication within 5G wireless communication systems. Hence, it is necessary to rethink the medium access control (MAC) protocol to address the massive number of devices accessing the shared medium and the limited-power and low complexity requirements of IoT devices.
Coordinated medium access protocols such as time-division multiple access (TDMA), frequency-division multiple access (FDMA), or code-division multiple access (CDMA) are contention-free protocols which ensure that resources are exclusively scheduled for each device. However, these protocols are not scalable and cannot provide sufficient throughput to meet the demands of a massive number of IoT devices due to the empty slots and the scheduling overhead required for the connection establishment before each transmission.
As such, uncoordinated random access protocols have attracted lots of attention in the standards as a possible method for enabling a massive number of M2M communication links using short packets possible, while maintaining a low signaling overhead. However, uncoordinated medium access protocols, such as Aloha and Slotted Aloha (SA) only perform well in small networks and cannot provide sufficient throughput in networks with many IoT devices that are simultaneously transmitting over the shared medium due to collisions at the IoT gateway.
Similar issues exist in IEEE 802.11, which is based on carrier-sense multiple access with collision avoidance (CSMA/CA), where collisions can still happen due to the hidden and exposed terminal scenarios. Moreover, CSMA/CA is not compatible with the limited-power requirements of IoT devices because it requires continuous channel monitoring.
The various MAC protocols known in the art fall short of achieving high throughput and a low channel-access delay for a large number of active IoT devices when the number of available radio resources is limited. Another drawback to MAC protocols known in the art is the high transmission power that is required as the number of active IoT devices increases, which makes them incompatible with power-limited IoT devices.
Accordingly, what is needed in the art is an improved MAC protocol for M2M communication that is scalable, matched to the limited-power requirement of IoT devices ad provides high throughput.